How to check server life using QWebsocket ping pong.

As @Christian-Ehrlicher mentioned, in this case you could just use a timer which is started when you send the ping, and then if no response has been received within x seconds you know that the server is most likely down.

I dont know how to do this.

Christian Ehrlicher

@bd9a said in How to check server life using QWebsocket ping pong.:

I dont know how to do this.

We won't write you your program. What exactly do you don't know? How to restart the timer? Did you read the QTimer detail documentation?

mrjj

Hi
well you hook up
void QWebSocket::pong(quint64 elapsedTime, const QByteArray &payload)
to a slot / lambda
then right after
you do
QWebSocket::ping(xxx)

then set up a timer


bool TimeOutbeforePong=false; // this should be a member of the class  owning the QWebSocket
QTimer::singleShot(5000, this, [ & TimeOutbeforePong ](){      
      TimeOutbeforePong = true;
    ... do something...
  });

if you get your Pong while TimeOutbeforePong is false, server is alive
and you can ignore the timeout.

or similar code.

BD9a

@kayote said in How to check server life using QWebsocket ping pong.:

and then if no response

How my program can know if no response, there is no bool "pongReceived" true or false.

@mrjj
Trying to implement it to my program. brb

mrjj

@bd9a
well the timer will trigger after 5 seconds (or what you set it to)
and if you did not see the PONG signal in the meantime, then
server is not answering.

You might want to make the timer a member so you can cancel/stop it but
you can also just ignore the flag if you get your pong

BD9a

@mrjj
I dont know connect

void QWebSocket::pong(quint64 elapsedTime, const QByteArray &payload)

to what?

    timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()),this,SLOT(trying()));
    timer->start(5000);

void Socket::trying()
{
    bool TimeOutbeforePong=false; // this should be a member of the class  owning the QWebSocket
    QTimer::singleShot(5000, this, [ & TimeOutbeforePong ](){
          TimeOutbeforePong = true;
          webSocket.open(QUrl("xxx")); // Can it be here?
      });
}

Christian Ehrlicher

@bd9a said in How to check server life using QWebsocket ping pong.:

to what?

To a function from you where you restart the timer...

BD9a

I need to access "TimeOutbeforePong" from other function, so I added it as private member, and I got these errors:

private:
    bool TimeOutbeforePong=false;

void Socket::trying()
{
    TimeOutbeforePong=false;
    QTimer::singleShot(5000, this, [ & TimeOutbeforePong ](){ // TimeOutbeforePong in capture list does not name a variable
          TimeOutbeforePong = true; // this cannot be implicitly captured in this context
    });
}

BD9a

Could sbody help me?

aha_1980

@bd9a

A short google for "lambda capture member variables" gave the following result:

https://stackoverflow.com/questions/7895879/using-member-variable-in-lambda-capture-list-inside-a-member-function

In short, you need to capture [this]:

QTimer::singleShot(5000, this, [this]() {

Regards